1. Field of the Invention
The present invention relates to a method and apparatus for preventing the overheating of a line feed motor for a printer due to line feed operation of printing paper.
2. Related Art
The following measures have been taken as methods of preventing the overheating of a line feed motor (hereinafter referred to as "LF motor") incorporated into a printer.
(1) Using a motor having a high rating, or using a motor provided with radiation fins to radiate heat so that the temperature of the motor will not exceed the rated temperature even if the motor is driven continuously during a continual line feed operation.
(2) Warning the operator in the operation manual of the printer that continual line feed operation for an extended period of time is forbidden.
(3) Detecting the temperature of the motor using a heat sensitive element and adding a necessary period of cessation to a motor driving cycle to enable the motor to cool when the temperature increases beyond an upper limit, as disclosed in Japanese Patent Publication No. 57-11041.
(4) Counting the number of line feed pulses representing the frequency of line feed operation in a fixed time limited by a timer and adding a period of cessation to the motor driving cycle to enable the motor to cool when the number of line feed pulses in a fixed time exceeds a fixed value.
These measures, however, have the following problems.
Measure (1) is planned against troubles which will not occur even if the motor is driven continuously for a long time which is scarcely necessary in ordinary operation of the printer and is never an efficient measure or, more properly, the measure provides the printer with unnecessarily high quality and increases the manufacturing cost.
Measure (2) is unable to prevent the overheating of the motor if the operator neglects the instructions or if the host computer controlling the printer malfunctions.
Measure (3) requires a heat sensitive element, which increases the cost of the printer.
Measure (4) adds a period of cessation to the motor driving cycle when the number of line feed pulses in a fixed time representing the frequency of line feed operation exceeds a fixed value, however, the measure does not take heat generated by the motor during acceleration and deceleration into consideration and hence lacks practical effect in preventing the overheating of the motor, because the current supplied to the motor for acceleration or deceleration is greater than that supplied to the motor during operation at a constant speed and hence increased heat is generated during acceleration and deceleration.